1. Field of the Invention
The present invention relates to a transmission/reflection type (hereinafter “transflective”) color liquid crystal display device having both reflection and transmission functions. A transflective color liquid crystal display device operates in a reflection display mode using ambient light from around the device under bright environments and in a transmission display mode using light from the backlight under dark environments. The liquid crystal display device of the present invention is suitable for use in various applications, including OA equipment such as word processors and personal computers, personal digital assistants such as electronic organizers, and camcorders with a liquid crystal monitor.
2. Description of the Background Art
A transflective color liquid crystal display device in portable equipment, etc., has a reduced power consumption and is capable of operating in a transmission display mode using a backlight, whereby it is suitable for use under various environments, and the use thereof as a display device in portable equipment, etc., is becoming widespread.
A conventional transflective color liquid crystal display device includes a color filter layered on a reflection film that is formed on a reverse-side substrate for producing a color display, and the reflection film is a transflective reflection film including light-transmitting openings in some portions thereof.
The color filter and the reflection film are formed within the liquid crystal panel so as to prevent the display color saturation from lowering due to the parallax caused by the substrate thickness, and a color filter with a high transmittance is employed in order to gain brightness in a reflection mode.
Other semi-transmissive reflection films include half mirror films obtained by thinning a metal such as aluminum or silver, those obtained by patterning a metal through an etching process so that portions thereof where the metal is left unetched are used in a reflection mode while other portions where the metal is removed are used in a transmission mode, and those utilizing interference which are obtained by layering dielectric layers of different refractive indices on one another.
One such liquid crystal display device is disclosed in, for example, Japanese Laid-Open Patent Publication No. 11-052366, where a color filter is layered on a reflection film that is formed on a reverse-side substrate, and the reflection film includes light-transmitting openings in some portions thereof that are opposing pixels of the color filter.
Japanese Laid-Open Patent Publication No. 11-183892 proposes a liquid crystal display device in which openings are provided in a color filter on a front-side substrate, a reflection film is provided on the inner surface of a back-side substrate in positions corresponding to the openings of the color filter, and a semi-transmissive reflector is provided on the reverse surface of the back-side substrate. It is stated that with this arrangement, it is possible to display an image through color pixels with a high brightness in a reflection display mode by using colored light that passes through portions of the color filter other than the openings and is reflected by the semi-transmissive reflector and non-colored light of a high brightness that passes through the openings of the color filter and is reflected by the reflection film, while it is possible to display an image through color pixels with a high contrast in a transmission display mode by outputting, to the front side of the device, only the colored light that has passed through the portions of the color filter other than the openings.
However, if a color filter with a high transmittance for gaining brightness in a reflection mode is employed in the liquid crystal display device described in Japanese Laid-Open Patent Publication No. 11-052366, although the display color saturation is high in a reflection display mode since light passes through the color filter twice, the display color saturation decreases considerably in a transmission display mode since light passes through the color filter only once. Moreover, if a color filter with a high saturation (low transmittance) is employed in an attempt to increase the display color saturation in a transmission display mode, the brightness in a reflection display mode decreases considerably, thereby lowering the visibility significantly.
The liquid crystal display device described in Japanese Laid-Open Patent Publication No. 11-183892 requires two reflection films. Moreover, reflected light from the reflection film on the inner surface of the back-side substrate and reflected light from the transflective reflector on the reverse surface of the back-side substrate are both used, thereby causing problems such as a decrease in the color purity due to the parallax caused by the presence of the back-side substrate.
The present inventors have found that when any of the layers of a transflective color liquid crystal display device provided on the viewer side with respect to the reflection film (e.g., a viewer-side substrate, an overcoat film, a liquid crystal layer, an alignment film, etc.) is colored in a particular color, a color displayed image as a whole is colored in the particular color not only in a reflection display mode but also in a transmission display mode, thereby causing a decrease in the color reproducibility, which has not been significant in a black and white display.
Moreover, in recent years, there is an increasing demand for reducing the thickness/weight of a transflective color liquid crystal display device. Accordingly, there has been an active research for commercializing a display device using a plastic substrate instead of using a glass substrate as in the prior art.
However, when a transflective color liquid crystal display device is produced by using a plastic substrate instead of using a glass substrate as in the prior art, a colorless and transparent plastic substrate gets yellowish in some cases through a production process such as heating during a color filter deposition, a transparent electrode film deposition or an alignment film deposition. In such a case, the color displayed image as a whole gets yellowish not only in a reflection display mode but also in a transmission display mode, thereby causing a decrease in the color reproducibility.